Add daily quota for precache

components/precache/core/proto/quota.proto

+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+syntax = "proto2";
+
+package precache;
+
+// Chrome requires this.
+option optimize_for = LITE_RUNTIME;
+
+// Quota limit and expiry time. This is stored in a database, and not
+// transferred via network.
+message PrecacheQuota {
+  // Represents the start time of this quota.
+  optional int64 start_time = 1;
+
+  // The number of hours since start time, this quota will expire.
+  optional uint32 expiry_hours = 2;
+
+  // Maximum number of bytes that can be fetched until this quota expires.
+  optional uint64 remaining = 3;
+};